Motor vehicle alignment systems are important for ensuring that the alignments of wheels on a vehicle are within the specifications provided by motor vehicle manufacturers. If the wheels are out of alignment, there may be excessive or uneven wear of the wheels. In addition, the performance of the vehicle, particularly handling and stability, may be adversely affected if the wheels are not properly aligned. As used herein, the term “wheel” or “vehicle wheel” refers to the tire and wheel assembly found on a motor vehicle. Such an assembly generally includes a conventional tire that is mounted on a metal wheel or “rim.”
The wheels of a motor vehicle may be aligned in a number of ways. For example, an operator or an alignment technician can use a vision imaging system such as a computer-aided, three-dimensional (3D) machine vision alignment system having optical sensing devices, such as cameras, to determine the positions of various objects. Although such machine vision systems are typically used for alignment purposes, these systems can also be used to obtain other positional and angular orientation information about a motor vehicle. Examples of such apparatus and methods are disclosed in U.S. Pat. No. 5,724,743, entitled “Method and Apparatus for Determining the Alignment of Motor Vehicle Wheels,” issued to Jackson, et al. on Mar. 10, 1998 and in U.S. Pat. No. 5,535,522, entitled “Method and Apparatus for Determining the Alignment of Motor Vehicle Wheels,” issued to Jackson, et al. on Jul. 16, 1996, each incorporated herein by reference.
Prior to measuring the alignment of a vehicle or performing the realignment of the wheels of the vehicle, it is standard practice within the industry to place the suspension of the vehicle in a “relaxed” condition. Devices commonly used for this purpose are low-friction turntables/turnplates and low-friction skid/slip plates. Prior to alignment, one or more wheels of the vehicle are placed on these devices, and the turntable and skid plate allow the vehicle wheel to turn and move both longitudinally and laterally to relax the forces on the wheels. Otherwise, if the wheels were not placed in a relaxed condition, misalignment of the wheels may create forces on the wheels that under or over exaggerate a misalignment problem, and the realignment of the wheels will not be based upon correct alignment data.
Notwithstanding that turntables and skid plates are used with alignment systems, these devices may be not always be properly used by an operator. Prior to positioning a vehicle onto a rack for measurement and/or realignment, the turntables and skid plates are locked into position. Once the wheels of the vehicle have been positioned on the turntables and skid plates, the turntables and skid plates are unlocked and the wheels allowed to float freely, which places the vehicle's suspension in a relaxed state. However, after the vehicle has been proper positioned onto the rack, a common error is that the turntables and skid plates are not unlocked prior to measurement of the alignment of the vehicle, and this creates the aforementioned problem of the realignment being based upon incorrect alignment data. There is, therefore, a need for an alignment system that controls the locking and unlocking of turntables and skid plates at certain times during the alignment of the wheels.